What is a good amount of money to save?

I don’t understand the premise; are you talking about how much money you would need to bring to survive in Germany or how much you intend to save while working here?

To live, it is at the lower level of what one would need to survive having a shared room and cooking your own food rather than eating out. Foreign students for example need to have 10,240 Euro as of 2020 for a year in a blocked account. But what is the context of your situation? As an American you can come as a tourist visa-free for 90 days but then need to leave for at least 90 days. One cannot simply come to Germany for a year and stay without the proper visa/residency status. And to get a work visa one needs to first line up a job and to get the employer do the extra paperwork.

If your question is meant as an intended amount to save while working here then it would not only depend on expenses but of course on your income. People often post on this site wondering about such a thing. They usually start with a minimal budget and expect that they can save lots of money but forget that miscellaneous expenses for travel, going out, simply having some fun once in a while can eat up most of what they intend to save.

The best amount of money to save is: As much as possible!